Incandescent electric lamp.



' @l lh ltflEm GEDBGE M. J. s'lIAGKAZZ, (2F NEW YORK, ASSIGNGR T0 GENERAL ELECTRIC A SUEZ-Iii RATION 0 NEW' YURK.

1N CANDESCEN'E ELECTRIC LAMP.

raaaoco.

No Drawing.

To all whom it may concern Belt-known that I, Gnoncn M. Jli/laonsr, a subject ofthe Kin of Great Britain, re SldlIig at Schenectar y, in the county of Schenectady and State of New York, have invented certain new and useful improve ments in Incandescent Electric Lamps, of which the following is a specification.

My invention relates to incandescent electric lamps and more especially to lamps provided with filaments of high melting point metals such as tungsten. in its preferred embodiment my invention is applied to lamps having filaments of drawn tungsten.

Among the objects of my invention is the production of a lamp in which the efiiciency of the lamp shall be maintained fairly cons'tant, and in which the length or" life of the lamp shall be greatly increased. his

result I accomplish in the particular embodiment hereinafter described, by providing within the lamp bulb a certain small pressure of a gas such as nitrogen, the pressure being so chosen that the tendency of the lamp to decrease in candle power as the filament wastes away and the lamp bulb blackens shall be more or less counteracted by the gradual disappearance to the so-called clean-up filament thereon. Where the amount of gas in the bulb is suitably proportioned in accordance with my invention, this clean-up action gradually removes gas from the space about the filament and thereby the cooling efiect of the gas upon the heated filament is decreased. There is thus a tendency for the temperature of the filament to rise, and if the amount of gas has been properly chosen in the first instance, this decreased cooling tendency may be made more or less closely to balance the tendency of the filamerit to fall in candle power as it slowly wastes away. 'this gas thus exerts a sort of equalizing efi'ect, for whereas it cools the filament at the beginning of its life, thus necessitating that the filament be run at higher temperature than in vacuum to give the desired efficiency, the cooling automatically becomes less as the lamp continues in operation and fall in candle power and in efiiciency is thus lessened or prevents Another factor in the reduction of ciency of an incandescent lamp'is the blackening of the bulb due to the deposition.

Specification of Letters Eatent.

Application filed April 3%, 1913.

Patented July 17, 1917.

Serial no. 764,701.

thereon of material evaporated from the filament. In the case of a tungsten filament lamp the color of this deposit is ordinarily black but in a lamp made in accordance with my invention the deposit, Where the filament is of tungsten, is distinctly brown, and appears to be tungsten nitrid '(Vi' li the nitrogen of the compound being derived from the nitrogen gas originally placed in the bulb. The nitrogen does not appear to combine directly with the metal of the filament but With the tungsten which has been driven cit" from the filament. The ueposit of nitrid lighter in color or tint than is the deposit in the case of a vacuum lamp, and therefore does not cut down so much the transmission of light, and this is a valuable feature in securing increased length of life of the lamp and maintenance of efiiciency.

The amount of nitrogen which I find it desirable to place in the bulb of the lamp varies according to the size and length of the filament, though the size of the bulb and the beneficial ellects of my invention may be.

obtained with pressures as low as one-tenth of a millimeter up to as high as 5 millimeters. With a filament of say 10' mils in diameter a pressure of about 25 millimeters may to advantage be employed, a higher pressure being allowable with filaments of large diameter on account of relatively less energy loss by conduction through the gas.

It is important that the pressure of nitrogen should not be too low, such, for example as a very small fraction of a millimeter, since in that case the clean-up effect is so rapid that the filament is left running at a higher temperature than it is capableol withstanding for a properlength of time, and the bulb discolors very rapidly. On the other hand, if too high a pressure of nitrogen is chosen, then the temperature of the filament, particularly if the filament be of small diameter, must be raised so high in orderto maintain proper efliciency that the lamp soon burns out. In general, the limits of pressure of gas to be'employed in the lamp in accordance with my invention may be roughly'placed as from one-fifth of a millimeter up to 50 millimeters for each square centimeter of filament surface, depending upon conditions, but the particular pressure to be employed in any particular case should be determined by the considerationswhich I have mentioned.

Where the pressure of nitrogen in the lamp is properly chosen, I have found that a lamp having a'filament of tungsten running in an atmosphere of this pressure has its useful life prolonged to some two or three danger due to arcing. between the leading-in wires m'the lamp.

'I am aware that lamps have been constructed in which a small amount of gas probably less than .025 millimeters was purposely allowed to remain in the bulb. After the-bulb had been thoroughly evacuated, the filament not having been brought to incandescence during this period, the bulb was sealed off so that thereafter, when the filament was heated to incandescence a certain amount of gas was driven out of the filament. This gas is sometimes known as the flash gas, consisting probably of carbon monoxid and hydrogen, and this gas remained in the bulb and was observed to have a certain beneficial effect, thenature of which was, however, not understood. In

those cases, however the improvement in the life of the lamp was only a few per cent.,

whereas in lamps made in accordance with my invention an improvement of 200 to 300 per cent. or more has been noted. Moreover, in those lamps to which I refer in which the flash gas had been allowed to remain, the appearance of thebulb after operation was radically different from that of the bulbs of lamps made in accordance'with my invention,-the deposit on the bulb being of a bliiish black color instead of a light brown.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In an incandescent electric lamp, the combination of a bulb, a filament therein of tungsten, and a low pressure of gas which is substantially chemically inactive with respect to the filament itself, the pressure being so chosen initially that the progressive clean-up of gas during the operation-of the lamp produces a progressivede'crease in cooling effect on the filament approximately counterbalancing the progressive decrease in heat generated in the filament, due to the ing of nitrogen therein at an initial pressure corresponding substantially to the proportion of about g; of a millimeter up to 50 millimeters of mercury pressure for each pressure progressively decreasing during the operation of the lamp.

3; An electric incandescent lamp comprising a sealedbulb, a tungsten filament therein, and a filling of gas'which does not directly attack the filament but which will form a compound with material driven off from the filament, the pressure of the gas being chosen initially to be about 10 millimeters of mercury pressure for every square centimeter of filament surface.-

. 4. An electric incandescent lamp comprising a bulb, a tungsten filament therein about 5 mils in diam eter'and about 5 inches in length and an initial pressure of nitrogen of about-2 millimeters of mercury, the nitrogen progressively decreasing in pressure with the hperation of the lamp.

.In witness whereof, I have hereunto set my hand this 28th day of April, 1913.

GEORGE M. J. MAOKAY.

Witnesses BENJAMIn B. HULL, HELEN ORFORD. 

